1. Field of the Invention
The present invention relates to a pump rotor capable of increasing a discharge amount and improving durability without increasing an outer diameter or an axial thickness of a rotor.
2. Description of the Related Art
In rotors of the related art such as a trochoidal gear used in an internal gear pump such as an oil pump, the number of teeth is practically restricted by specifications such as a dedendum diameter of an inner rotor and an amount of eccentricity relative to an outer rotor. Thus, the number of teeth can be increased or decreased within a narrow range. Moreover, if the dedendum diameter, amount of eccentricity, and number of teeth described above are determined, a theoretical discharge amount is practically determined.
In a trochoidal rotor of the related art, in order to increase a theoretical discharge amount, a method of increasing an amount of eccentricity between an inner rotor and an outer rotor to increase the diameter of the rotor, or increasing the thickness of the rotor without changing the amount of eccentricity and the rotor diameter is used. However, in either method, the rotor size increases, which may deteriorate frictional properties.
Japanese Patent Application Laid-open No. 2011-17318 discloses an example of a technique for solving such a problem. The invention disclosed in Japanese Patent Application Laid-open No. 2011-17318 will be described briefly. First, the invention relates to a rotor in which the degree of freedom in setting a tooth height is increased to increase a theoretical discharge amount of a pump. Moreover, a plurality of ellipses that form the tooth profile includes a predetermined number of combinations of ellipses that have an appropriate size such that formed teeth have a larger tooth height than that of an inner rotor that uses cycloidal curves or trochoidal curves to form a tooth profile thereof.
As in the configuration described above, in the inner rotor, an ideal tooth profile is obtained by forming each of the tooth profiles of an addendum portion, a dedendum portion, and an engagement portion (a portion that connects the addendum portion and the dedendum portion) that engages with an outer rotor using a curve (a curve having a larger radius of curvature) that extends along the longer axis of an ellipse.
In a tooth profile of FIG. 4 disclosed in Japanese Patent Application Laid-open No. 2011-17318, an addendum portion 2a and a dedendum portion 2b are formed both by a curve that extends along the longer axis of an ellipse. Thus, it is possible to increase the areas of the addendum and the dedendum in contact with the teeth of an outer rotor and improve a protection effect of the addendum and the dedendum. Moreover, as shown in FIG. 4 disclosed in Japanese Patent Application Laid-open No. 2011-17318, by forming an engagement portion 2c using a curve that extends along the longer axis of an ellipse, it is possible to sufficiently increase a tooth height h.
A rotor of an internal gear pump disclosed in Japanese Patent Application Laid-open No. 2011-17318 will be compared with a general rotor that uses trochoidal curves. FIG. 12 disclosed in Japanese Patent Application Laid-open No. 2011-17318 shows a pump rotor in which an inner rotor having eight teeth and an outer rotor having 9 teeth are combined.
Specifications of the tooth profile of Japanese Patent Application Laid-open No. 2011-17318 are shown below.
Outer Diameter of Outer Rotor: φ60.0 mm
Large Diameter of Outer Rotor (Dedendum Circle Diameter): φ52.0 mm
Small Diameter of Outer Rotor (Addendum Circle Diameter): φ38.4 mm
Large Diameter of Inner Rotor (Addendum Circle Diameter): φ45.2 mm
Small Diameter of Inner Rotor (Dedendum Circle Diameter): φ21.6 mm
Inner Diameter of Inner Rotor: φ15.0 mm
Rotor Thickness: 15 mm
Amount of Eccentricity e: 3.4 mm (Tooth Height 2e: 6.8 mm)
A theoretical discharge amount of the internal gear pump disclosed in Japanese Patent Application Laid-open No. 2011-17318 is 12.3 cm3/rev.
As a comparative product for the internal gear pump disclosed in Japanese Patent Application Laid-open No. 2011-17318, a pump rotor having a tooth profile that uses trochoidal curves shown in FIG. 15 disclosed in Japanese Patent Application Laid-open No. 2011-17318 is used. FIG. 15 disclosed in Japanese Patent Application Laid-open No. 2011-17318 shows a pump rotor having a tooth profile of the related art. The specifications of the comparative product are shown below.
Outer Diameter of Outer Rotor: φ60.0 mm
Large Diameter of Outer Rotor: φ52.0 mm
Small Diameter of Outer Rotor: φ39.6 mm
Large Diameter of Inner Rotor: φ45.8 mm
Small Diameter of Inner Rotor: φ33.4 mm
Rotor Thickness: 15 mm
Amount of Eccentricity e: 3.1 mm (Tooth Height 2e: 6.2 mm)
A discharge amount of the comparative product is 11.4 cm3/rev.
Consequently, the rotor disclosed in Japanese Patent Application Laid-open No. 2011-17318 has a larger tooth height than that of the comparative product by extending the tooth height toward the inner side. Moreover, the theoretical discharge amount is increased.
As described above, Japanese Patent Application Laid-open No. 2011-17318 discloses a rotor of which the theoretical discharge amount is increased by increasing the tooth height. Moreover, in order to increase the tooth height, each of the tooth profiles of the addendum portion, the dedendum portion, and the engagement portion is formed using a curve that extends along the longer axis of an ellipse so that an ideal tooth profile is obtained. However, since the tooth profile is formed using ellipses that are smaller than a formation tooth profile, ellipses that partially overlap each other are connected approximately at 90°. The radius of curvature decreases near the inflection point of a connecting portion between a circular arc of the addendum and a circular arc of the engagement portion, the shape changes abruptly, and the tooth profile is not sufficiently smooth.
Moreover, since the teeth angle of the engagement portion increases due to an increase in the tooth height, an engagement range between the engagement portion and the outer rotor decreases. As a result, a force that presses the outer rotor is concentrated on a small area, and surface pressure increases. Moreover, since the outer rotor is driven in a state where a sliding factor is large, durability decreases. Moreover, since the addendum of the inner rotor and the dedendum of the outer rotor are closely situated in a large area of a deepest engagement portion, oil may be unable to find its way when the oil is discharged, and pumping loss increases.